A resistance change memory is known as a kind of semiconductor memory device. A magnetoresistive random access memory (MRAM) is known as a kind of resistance change memory. The MRAM features a high-speed operation, a large capacity, and nonvolatileness, and has been researched and developed as a next-generation memory device that replaces a volatile memory such as a DRAM or SRAM.
In the MRAM, a magnetic memory device using a tunneling magnetoresistive (TMR) effect is used as a memory cell for storing information. As the magnetic memory device, an magnetic tunnel junction (MTJ) element having a stacked layer of metal magnetic film/insulating film/metal magnetic film is used. A change in the resistance of the MTJ element is determined by the magnetization states of the metal magnetic films that sandwich the insulating film. That is, the MRAM stores data according to the magnetization state of the MTJ element.
The characteristics of the MTJ element are represented using a write current, a magnetoresistive ratio (MR ratio), and the like as indices, and are affected by the processes of forming the MTJ element. The characteristics of the MTJ element lower or vary due to the influence of, for example, the planarity of an underlayer used when stacking layers or the element isolation process of the MTJ element. To reduce a write/erase current and improve the MR ratio while ensuring a high data retention characteristic, it is necessary to improve the structure and manufacturing method of the MTJ element.